Question

I have two tables:

Table 1: CustomerEmails:

CREATE TABLE [dbo].[CustomerEmails](
    [id]            [int] IDENTITY(1,1) NOT NULL,
    [datecreated]   [datetime] NULL,
    [UID]           [nvarchar](250) NULL,
    [From]          [nvarchar](100) NULL,
    [To]            [nvarchar](100) NULL,
    [Subject]       [nvarchar](max) NULL,
    [Body]          [nvarchar](max) NULL,
    [Dated]         [datetime] NULL,
 CONSTRAINT [PK_CustomerEmails] PRIMARY KEY CLUSTERED 
(
    [id] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
)

Table 2: CustomerEmailIds:

CREATE TABLE [dbo].[CustomerEmailIds](
    [Email] [varchar](200) NULL
) ON [PRIMARY]

You may be thinking that why i am not using the EmailId in table CustomerEmails instead of using the emails itself? what i mean is that i can add a column EmailId (INT) to the table CustomerEmailIds & then i can refer that column instead of CustomerEmails.From & CustomerEmails.To?? Guys the issue is the table CustomerEmails is used by some other application & that application just keeps the track of emails sent/received through OutLook. The table CustomerEmailIds have customer emails & these emails come into system from the application i am working on.

So the Table CustomerEmails have 7,00,000+ records while table CustomerEmailIds have 1,00,000+ records.

I need to find out the emails from table CustomerEmails, based on the emails in CustomerEmailIds table.

The query i am using is:

SELECT  
        e.*
FROM    CustomerEmails e 
WHERE   EXISTS 
        (
            SELECT  Email 
            FROM    CustomerEmailIds c 
            WHERE   ( ISNULL(e.[From],'') + '/' + ISNULL(e.[To],'') ) LIKE  '%'+c.Email+'%' 
        )

Some facts:
1- I am using SQL Server 2008
2- Sorry guys, i forgot to mention that the CustomerEmails.**To** can contains multiple comma separated emails like: [e-mail],[e-mail],[e-mail]
3- Because of the fact2 the c.Cs3Emails+'%' OR to= c.Cs3Emails will not list the desired results that's why i am using '%'+c.Cs3Emails+'%'

Latest Findings:
Guys the above query return wrong results….. & i don’t know why??

But below query works fine:

SELECT  
    e.*
FROM    CustomerEmails e 
WHERE   (ISNULL(e.[From],'') + '/' + ISNULL(e.[To],'')) LIKE  '[e-mail]%' 

Answer 1

Well guys first look at the query which is returning the wrong results:

SELECT  
        e.*
FROM    CustomerEmails e 
WHERE   EXISTS 
        (
            SELECT  Email 
            FROM    CustomerEmailIds c 
            WHERE   ( ISNULL(e.[From],'') + '/' + ISNULL(e.[To],'') ) LIKE  '%'+c.Email+'%' 
        )

There is no issue in this query, the issue is that some of the emails in CustomerEmailIds table are invalid emails which are (‘.’,’@’,’0′,’-‘) & that’s why the query is returning all the CustomerEmails where these invalid emails exists.

Thanks to Kev Riley! the persons who helped me find out the cause of this issue here!